Abstract: Roof is one of the main structures of a building,and it plays an important role in improving the degree of indoor thermal comfort so as to reduce the using of air-conditioner.Through a contrastive study on the water-storing green roof and the common roof in a certain living district in Xiangtan city,the article comes to the conclusion: the water-storing green roof not only can enhance the urban eco-environment,but also can modulate the indoor thermal property and decrease the using of air-conditioner,so it is a comprehensive method to save both water resource and energy and can be popularized in the south urban areas.